Television receiver



Feb. 17, 1942. D. o. LANDIS TELEVISION RECEIVER Filed Deo. 30, 1938 4Sheets-Sheet l :inventor 0. L an di' Daniel N .www

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dtrorneg Feb. 17, 1942. v D. o. LANDIS 2,273,801

TELEVISION RECEIVER Filed Dec. 30, 1958 4 Sheets-Sheet 2 M/Hnon v t?/acREEN Imca/VER afwas/.s d] 22 n] 20 l @E18 Z0 x ,i7 I Wl E l .I'A16//l m17 15 12 l .a/ Z1 7 l/ lnoentor Daniel 0. Lan/dus t 'PatentedFebltlvh1 942 I fija-,213,801 c u fr ELEylsIoN REcErvEE Landis, UpperDarby, Pa., .assigvnor '1 of America, a 'corporation ppl'iatqinecembef4so, 193s, seal 1410.248569 f ,1-3 ,Chi-ms. CL 173:15)

My invention relates to television receivers or the like andparticularly to television receivers of the projection type. c Indesigning television receivers of' the projection type employing acathode ray tube, one of the principal ldiiliculties has been inobtaining a good qualit-y'projected picture which is su`fl`1'cientlybright. A- Itis, accordingly, an object of my invention toprovide an improved television receiver which will reproduce a pictureof comparatively large.

sizeand of the desired brilliancy.

In practicing my invention I employ a spherical mirror for projectingthe image appearing on a fluorescent screen, and provide a correctingplate to eliminate substantially all spherical aberration.

It'v has been previously proposed'v to project a l of a televisionreceiver embodying my invention,

Figure 4 is a view, partlyin section, of a portion of the receiver shownin Fig. 3, I

Figure 5 is aview taken on the line Fig. 4, and

Figure 6 is a view illustrating another embodi` ment of myinvention.

Referring to Fig. -1v, -therefis illustrated yafspecic optical systemwhich maybe employed in a television receiver embodying my invention,y-specic dimensions being givenY merely by Way of example. Thesystemcomprises a spherical 'mire' ror l and acorrecting plate 2.' The'end ofthe cathode ray tube upon which the picture appears is indicatedat 3 while the`s'creen upon which ther picture is projected is indicatedat 4.

Thel correcting plate is guredoto bring light' rays reflectedliromeither theedge of the mirror for example, orhigher without anynoticeable spherical aberration, "chromatic laberration or coma. Inother words, I provide a fast lens sys,-

tem of vhigh duality. Furthermore, it ris a lens system which absorbs aminimum amount of the light produced by the cathode ray tube.

As will be explained in detail hereinafter, the correcting plate 'andspherical mirror combination resembles the Schmidt camera which'is usedin astronomical work. However, in my system the correcting plate isground or gured for a finitedistance frommirror to projection screenwhereas they corresponding distance -in the Schmidt camera is infinity.Also, the object surface `f the fluorescent screen) inv my optical'system asfconstructed up to this time does not, as v in the Schmidtcamera,"havearadiusV equal -to half theradius of the spherical'mirror,but, in::

stead,l it has a curve which will focus any Apoint;y

on `itsy surface on the image `surfacerwhichzordinarilyis'a projectionscreenvhaving a plane sur` face. f I The invention will be betterunderstood from the following description,` taken in connection withtheaccompanying drawingsin which Figures 1 and 2 are diagramsn which arerev ferred toin describing theoptical. systemv enfi-A-`v ployed in myimproved receiver.

Figure 3 is a view, drawn substantially'to scale,"l

Y` projectionk screen,

or from a point 'on or near its axis into focus at the projectionscreen.

any one of several shapes although 4theshape illustrated is preferred.The way in which the correcting plate functions'mis illustrated in Fig.42.

Referring to Fig. 2*, it is assumed there is a light source at thepointmarke'd focuslff' Light rays from this source-reected from themirror ,l nearits edge would have their focus atthe point' marked normaledge focus" in theabsenc'e of the correcting plate 2. The correctingplate, however, is figured to refract these edgerays just enough to makethem focus on theprojection f screen 4.

Considering the axial rays from the same light" source, it will be vseenthat in the absence of the correcting plate .they focus at the pointmarked normal axial focus.v The correcting'plate is f gured to refractthese rays the correct amount to make them focus on the screen-4.7Ihuslthe correcting plate may be sogured as rto. make all rays originatingfrom this light source andre-- to a `focus onf-the ected 'from` themirror come Considering rays or object 3 ofi;I the axis, the raysyfiomac'orn'er of the',` picture in' order to l'foc'zi'isfonits correspondingcorner ofk the screen l mustv have a? `shorterobjet focus andy alonger-image focus n Therefore, the v* radius of the object surface 3-will be greater than thefaxial or central rays.

than one-half theradius ofI the mirror 'I-. Thus, in theoptical systemAshown` infFig. l*

v c As m the case' of thev i Schmidt camera, the correcting plate mayhave from a point 'on the 'picture/' lit 'was klvfound that'the' radiusof curvatureforftlrie' fluorescent screen on theiend yof the tube shouldbe* inches where the radius of curvature of the spherical mirror was171/4. inches.

The curvature of the object surface 3 may not be exactly. spherical insome cases but'it will be very Vnearly so'. 0f course, this curvatureshould be changed if the screen 4 is given. a curvature instead of beingflatas it ordinarily is. v

TheA desired curvature for the object surface I may be obtained by`placing a photographic plate on the axis of the optical system and thentracing a curve thereon by moving a spot of light, such as an electricbulb, along the projection screen and in a direction parallel to theplane of the photographic plate.

For example, referring to Fig. l, a. photographic plate may bepositioned, at the focus between the mirror i and the correcting plate 2with the emulsion side up, i. e.,`the photographic plate is in the pianeof the paper. Then the light from an electricrbulb moved horizontallyalong the image surface I (i. e., moved in the planeof the paper)focuses on the photographic plate and traces the desired curve.

As to the technique employed in figuring and testing the correctingplate, it may be noted that, since my projection system focuses at afinite distance, it was found desirable to employ a testing procedureduring the figuring of the plate based on the fact that the longitudinalspherical aberration of a high aperture mirror and the diameter oi' thepupilv ofthe eye will make light from a pin hole at the focus appear tothe eye placed on the axis at the second focus as a bright ring on thesurface of -the mirror. If the eye is placed on the axis at a pointcloser to the mirror, a ring of light of larger diameter on the mirrorwill be seen.

If we take a series of these annular zones or rings each having a focuson the axis and figure the correcting plate to bring them all to a focusat the same point, we have the required curve on the correcting plate.Thus, the procedure may be as follows:

Bet up the system minus the correcting plate and, after placing a markon the mirror at about Surface.

.7 the distance from the center of the mirror to its edge, move the eyealong the axis until the bright ring visible on the mirror passesthrough this .7 point. Adjust the foci until the bright ring passesthrough the .7 zone when the eye and pinhole are at the desiredconjugate foci. AWhen these adjustments are acquired, the bracket usedfor holding the correcting plate is placed so that first principal planeof the plate is at the center of curvature of the main mirror. A rayfrom the .7 zone of the main mirror should pass through the finishedcorrecting plate without deviation and fall half waybetween the maximumand minimum foci of the uncorrected main mirror.

The reason forA working from a zone'.7 of the distance from the centerof the mirror to its edge is that the area of the mirror inside this .7ring is about equal to the mirror area outside this ring. Thus, thecorrecting plate may be figured to have a positive power for half thelight andv a negative power for the other half of the light whereby therefracting angles of the plate will be at a minimum for the desiredcorrection. For all practical purposes, the .7 measurement may be takenon the chord from the center of the mirror to its edge. v

vI'he area of the correcting plate inside the .7 ring is then masked ofiand the negative power of the edge zone or .3 zone is increased bygrindscreen about 2 inches inside the focus.

does the center or .7 zone. l 'This edge zone, of

course, is the area betweenf'the .7 ring and the edge of the mirror.

The progress of the grinding of the edge zone is checkedfrom time totime by looking at the mirror from a point on the axis and noting thechange in the position from which a certain ring of light is seen (thisposition being the focus for this particular ring of light). l'orAexample, if the eye is located on the axis at thepoint marked Normaledge focus (Fig. 2), a bright ring is seen near the edge of the mirror.After the edge zone has been Worked on some by the grinding machine, itwill be found that this ring of light is now seen from a point closer tothe desiredcommon focus. When this ring is seen from the desired commonfocus, the correction' for the particular zone of the correcting platethrough which this ring of `light passes has been completed.

During the grinding of the edge zone, the other light rings of smallerdiameter should be observed from time to time just as described inconnection with the ring of largest diameter. When the rough grinding ofthis zone is finished, the entire edge zone will appear from the commonfocus to be covered with narrow rings.

After the edge zone is made to focus at the correct place, mask ofi'this zone and work on the center or .7 zone and increase the positivepower over this area until the rays falling beyond those of the .7 zoneare brought into focus at the same place as those from the rest of theIn order to generate a curve continuous with that of the edge, it isbest to workon the center portion beginning at the .7 zone.

It will be understood that the grinding of the center zone is checked insubstantially the same way as described in connection with the grindingof the edge zone.V

So far we have the general rough curve generated on the plate and wewill find the entire surface covered with narrow rings. It is necessaryfrom the beginning of this grinding operation to see that the plate isperfectly centered and running true on the grinding machine and frequentchecks should be made to determine that the plate is maintaining a truesurface of revolution.

It will be found that very narrow zones'are capable of becoming tiltedin relation to the general curve and may be detected by holding a Abright ring from a tilted zone will appear eccentric to the rest of thepattern. If the screen is moved to within a few inches of the plate andthe finger used to cast a shadow, the zone responsible for the eccentricring can be covered with the finger and the shadow followed from theplate to the focus as the screen is moved away. The tilted zoneresponsible for the ring can be interpreted into the direction of tilton the surface of the plate which would cause the deflection of anannular cone of light creating the eccentric ring as found. Due to thefact that all errors appear in complementary illumination on oppositesides of the focus, it is best to do all testing inside the focus.

After the direction of tilt hasbeen determined and the high portionlocated (by a scale placed in front of the correcting plate and by acorresponding one on the grinding machine), the plate is tilted on theturntable so that most work will be ing until this zone focuses at thesame place as done on this zone,

'I'he machine is arranged so that pressure is lncreased when the highzone comes under the grinding tool. After most of these narrow zoneshave been corrected, the plate, after being indicated true, is worked onwith the largest tool possible with a radial stroke and the remainingnarrow zones averaged out.

If desired, after the correcting plate has been figured as describedabove to bring all zones of the mirror close to the desired focus, astandard test such as the Foucalt knife edge test may be employed forfiguring the correcting plate still more accurately.

It was found that much time could be saved by coating the ground surfaceof the correcting plate with glycerine eachv time it was desired to makea test to permit testing without having to grind the plate to a smoohsurface.

One practicalembodiment of my invention is illustrated in Fig. 3.

Referring to Fig. 3, the television receiver comprises a cabinet I Il ofthe console type having a translucent screen Il, such as ground glass,in

the front thereof upon which the reproduced picn ture is to appear.

A cathode ray receiver tube I2 ofthe projecthe center of curvature ofthe mirror I4 to bring the light rays originating at the fluorescentscreen I3 and reflected from the mirror I4 to a focus on the screen IIas explained in connection with Fig. 2. A mirror I9 is mounted at 45degrees to direct the light rays from the correcting plate I8 to thescreen II.

Preferably, adjusting screws 20 are provided to facilitate axialadjustment of the correcting plate I8.

The loud speaker 2I and the receiver chassis 22 may be located in thereceiver cabinet as indicated. With the above described receiver, abright picture 15 inches by 20 inches of good quality may be obtained.It is assumed, by way of example, that the optical system of thisreceiver has the dimensions given in Fig. 1, the effective aperturebeing approximately .6.

It will be understood that the receiver shown in Fig. 3 may be designedto project a still larger picture upon a separate projection screenplaced across across the room from the receiver, for example. In thiscase, the screen II is removed from the cabinet I0. Obviously. thecorrecting plate I8 should be figured differently for the differentconjugate foci.

The mounting and adjusting means for the cathode ray tube I2 of Fig. 3are shown more clearly in Figs. 4 and 5. The mounting supports I6 are inthe form of a spider comprising four metal straps attached at their endsto thel shelf I5. A metal cylinder 35 is welded or otherwise fastened tothe inner ends of the spider arms I6.

The cylinder 35 has extending upwardly therefrom three lugs 36 forsupporting the connecting plate I8 at the center. desirable where theplate has been molded from a plastic such as Lucite.

The lower part of cylinder 35 has two slots'31 therein in whichadjusting screws 38 may slide.

The tube I2 is supported from the cylinder 35 Such support may be lli)wedge member 42 fits into the small spacev between the neck of the tubeI2 and the. yoke I1, the wedge being secured to the neck of the tube bya clamp 43.

The tube I2 and deecting yoke .I1 are supported from the cylinder 35 bymeans of a cylindrical member 46 which telescopes into cylinder 35 andis held in position by means of the screws 38.

The lower end of member 46 has an edge 41 spun or otherwise formedthereon which has a spherical surface conforming to the surface ofmember 4I. Adjusting and fastening screws 48 pass through openings inthe edge 41 and fasten in the member 4I in screw threaded relation, thesaid openings being large enough to permit .an adjustment of the tube I2about its lower end as a pivot.

From the foregoing, it will be apparent that by loosening the screws 38the tube I2 may be moved axially to different positions, as indicated bythe dotted lines, for the purpose of focusing the image upon theprojection screen. Also, it will be seen that by loosening the screws 48the tube I2 may be adjusted about the center of the lower end of thetube as a pivot point whereby the edgesof the picture may readily bebrought into focus.

In Fig. 6 there is illustrated another embodiment of my invention, thisreceiver being designed to project a picture upon a screen indicated' at28. In this figure the screen 26 is shown much ytco close to thereceiver because of limited space on the drawing.

The receiver comprises a cabinet 21 which may beeither of the tablemodel or console type. A cathode ray tube 28 is positioned in front of aspherical mirror 29 in the proper relation to project the imageappearing on the end* of the cathode ray tube upon the screen 26. Acorrecting plate 3I, as previously described, is mounted at the front ofthe cabinet. The tube 28 preferablv is adjustably mounted as previouslydescribed.

If the cabinet is of the console type as illustrated, the loud speakermay be located inthe lower part of the cabinet as indicated at 32 orremotely, as desired. The receiver chassis 33 may be mounted in the topof the cabinet as shown, or it may be located along one side of thecabinet if 'the cabinet is made of suilicient width.

ceive the light issuing from the source, an l aspherical zone platepositioned to receive the reflected light projected from thelightsource, said zone plate being arranged external to the light path fromthe light source to the reflector and axially aligned with each andadapted to correflected light rays by the reflecting surfacel whereby asharply focused enlargement of the original finite dimension lightsource is developed at a plane located at a finite distance from theaspherical zone plate. y

2. An image projection device comprising a light source of flnitebi-dimensional image area emitting light according to Lambert's law, anaxially aligned optical system including a concave reflecting surface ofrevolution positioned to receive the light issuing from the source, andan aspherical zone plate positioned external to the path of the lightprojected from thelight source to the reflector and positioned toreceive the reected light from the reflector, said zone plate beingadapted to correct for spherical aberrations introduced by thereflecting surface whereby the optical system projects a sharply definedenlarged image substantially free from spherical aberration upon aviewing surface located at a finite distance from the zone plate.

3. An image projection device comprising a cathode ray tube to produce alight image, and an aligned optical system including a sphericalreflector element having its concave surface area positioned to receivethe light image from the tube and an aspherical zone plate located atsubstantially the center of curvature of the spherical reflector elementto receive the light image as reflected thereby, said zone plate beinglocated external to the light path from the tube to the reflector andhaving such curvature as to correct for spherical aberration introducedinto the reflected light rays by the reflector whereby the opticalsystem including the reflector and the zone plate is adapted to form aprojected enlarged image of the light image upon the cathode ray tubeupon a viewing area located at a flnite distance from the zone plate.

4. A television image projection device comprising a cathode ray tubehaving a luminescent target area whereupon an optical image is produced,a spherical reflector` having its concave surface area positioned toreceive the light of the image as produced upon the cathode ray tube, anaspheric zone plate located externalto the tube to reflector opticalpath and arranged to receive the reflected light from the reflector,said zone plate having its surface area of such curvature as to correctfor spherical aberration due to the reflector so that a sharply focusedenlarged image of the tube target area may be focused upon a viewingsurface located at a finite distance from the zone plate.

5. The device claimed in claim 4 wherein the said zone plate is locatedsubstantially at the center of curvature of the reflector.

6. In a television image projecting and enlarging apparatus, a cathoderay tube having means to produce light representative of an image, analigned optical system to receive the light image on the tube, saidoptical system. in cluding a substantially spherical light reflectingelement having its concave surface positioned to receive the light fromthe light source, and an aspherical plate member located external'to thetube to reflector light path to receiv the reflected light from thereflector and located near or at the center of curvature of thereflector, said aspherical member being so curved as to correct forsphericalV aberrations introduced by the reflecting means, said platecurvature being such as to reduce the said spherical aberration to aminimum in a viewing area located a finite distance from the said platemember.

7. The apparatus claimed i'n claim 6 wherein the said aspherical platemember has a central aperture and wherein at least a portion of the saidcathode ray tube projects through the said plate.

8. The apparatus claimed in claim 6 comprising in addition means forpivoting the-\cathode ray tube about a pivot point located substantiallyat the center of the thereupon produced light image to adjust the saidtube relative to the light reflecting and projecting elements of theoptical system.

9. A television image projector and enlarger comprising a cathode raytube having a luminescent target area of ilnite dimensions whereupon atwo dimensional optical image is adapted to be produced, said opticalimage being adapted to radiate light substantially according to Lambertslaw, a substantially spherical light refleeting means yaxially alignedwith the axis of the tube and so positioned that the light rays of theimage upon the tube are adapted to fall upon the concave surface of thereflector, and a spherical aberration correcting means for correctingfor spherical aberration introduced by the said spherical lightreflecting means, said means comprising a zone plate member having itssurface of predetermined curvature to compensate for the said vsphericalaberration distortion and spaced from the reflector by a distance.approximately equal to the radius of' curvature of the reflector, saidzone plate being located external to the light path between said cathoderay tube and the reflector and so positioned that the said tube masksonly the central area of the said plate, whereby the optical system isadapted to focus an enlarged projected image of that upon the tube upona viewing surface located at a finite distance from the light source andoptical system.

10. In a television image projecting and enlarging apparatus, a cathoderay tube having a neck portion and a target portion whereupon an opticalimage is adapted to be produced, an optical system aligned with the tubeaxis, said system including a substantially spherical reflecting elementpositioned to receive the light from the tube target, and an aberrationcorrecting zone plate element located substantially at the center ofcurvature of the reflector and having its surface so curved as tocorrect for spherical aberrations introduced by the reflecting means,said surface being positioned externally of the light path between thelight source and the reflector and arranged to receive light dlrectlyfrom the reflector, said plate being also so curved that the sphericalaberration is a minimum upon an image viewing area located at a ilnitedistance from the optical system.

11. The apparatus claimed in claim 10 wherein said zone plate has itscentral area apertured and wherein the said tube neck is projectedthrough the plate aperture.

12. The apparatus claimed in claim 10 comprising in addition means forpivoting the cathode ray tube about a pivot point located substantiallyat the center of the thereupon produced light image to adjust the saidtube relative to the light reflecting and projecting elements of theoptical system.

13. In television image projection apparatus, a cathode ray tube devicehaving a luminescent target area and means to produce on the target,

near or at the center of curvature of the light l0 reflecting element,said surface being positioned externally of the light path between thecathode ray tube light source and the reflector and arranged to receivelight from the reector, and said optical system being adapted to focusthe enlarged image sharply and with minimum` spherical aberration upona, viewing plane located at finite distance from the correction plate.

DANIEL O. LANDIS.

